1. Field of the Invention
The present invention relates in general to color grading of gemstones. More particularly, the present invention relates to a method and system, including a computer program product, for implementing a color terminology in color grading of gemstones.
2. Description of Related Art
Colors of gemstones are usually graded visually against discrete color samples. For example, U.S. Pat. No. 1,617,024 to Munsell describes color chips. U.S. Pat. No. 4,534,644 to Beesley describes simulating color standards. U.S. Pat. No. 4,527,895 to Rubin describes reference color charts. U.S. Pat. No. 5,005,971 to Davis describes resin color chips, and U.S. Pat. No. 5,143,212 to Roberts describes simulated gemstones.
In known gemstone color grading, the color of gemstones can only be approximately graded using the above-referenced patented methods and systems typically using discrete color samples. In practice, each color grade represents a large or very large volume in color space for the discrete color samples. Thus, such methods or systems for color grading of gemstones are not accurate because of the occupation of significantly large volume in color space for each color grade. For example, two gemstones with the same known color grade based upon know methods and systems may actually have a very large color difference. Therefore, the two gemstones may show totally different perceptual colors, such as a dark brown color and a red color.
Several devices were patented for measuring colors ranging from colorless to light yellow for diamonds (D-Z color scale). U.S. Pat. No. 4,056,952 to Okuda describes a colorimeter, and U.S. Pat. No. 4,508,449 to Okazaki describes a spectrophotometer. U.S. Pat. No. 6,473,164 to DeJong et al describes a color device assigned to the Gemological Institute of America (GIA).
Both the Okuda colorimeter and the Okazaki spectrophotometer use an integrating sphere to measure the color, but their accuracies are not high enough for color grading of colors ranging from colorless to light yellow in diamonds. The GIA color device simulates the condition of human visual color grading for colorless to light yellow diamonds, but the detector does not have the basic function of self-focus of the human eye. Further, the fluorescent daylight tube is not stable enough for color measurement. Thus devices such as the GIA color device are not accurate for the purpose of color grading for colorless to light yellow diamonds.
U.S. Pat. No. 5,615,005 to Valente et al describes an imaging device for evaluating gemstones. The evaluation includes color grading of gemstones. The Valente device utilizes a band pass filter and a detector array to obtain spectral photometric data for each individual pixel of a complete color image for evaluating gemstone. However, this device is not well accepted by the jewelry industry since it does not accurately grade the color of the gemstones. The band pass filter may not be very stable in general, and the device may not be well profiled for color processing and color display.
GIA produced a color image device called ColorMaster for color grading of gemstones. The ColorMaster has three primary R, G and B knobs for adjusting the color of a simulated gemstone image. Due to the ColorMaster's original design problems, it is not suitable for color grading of gemstones. For example, it may result in a significantly large color shift for each ColorMaster due to no user calibration, thereby resulting in large color differences among different ColorMasters. In addition, the GIA color description system is not well defined in color space, and is awkward for verbal communication purposes. The ColorMaster has been abandoned.
Recently, GIA has been utilizing a software named Gemewizard to assist students in the teaching of its Colored Stones courses using the GIA color description system for colored gemstones. The software displays each hue page with about 36 separated color images. However, the software can only display discrete color images. Further, each color grade represents a large volume of color space. Thus the true color of a gemstone cannot be graded by the Gemewizard software.
The International Color Consortium promotes standardizing color management by color profile. The color profile defines how color can be rendered accurately. Color profiles can be used to display accurate colors in computer monitors. U.S. Pat. No. 5,619,349 to Ueda et al describes a device for calibrating display color of a CRT to a color standard, and U.S. Pat. No. 6,853,387 to Evanicky et al describes a system for compact flat panel color calibration. Several commercial available devices can be used to calibrate color monitors for accurate color display.
In Kelly et al Color: Universal Language and Dictionary of Names, NBS Special Publication 440, U.S. Government Printing Office, Wash., D.C., (1976), a method of designating colors and defining color names in the Munsell color space is introduced. Color terminologies used for color grading of gemstones are usually concerned with the fineness of level 3 for color designation. The GIA colored diamond grading system (see King et al, Gem & Gemology, 1994) for example, has only nine color grades for each hue, and about half of the grades are concentrated in a very small volume in color space with low saturation and high lightness. Other color grades cover a very large area. Each color grade actually represents a very large range of colors. Thus, known color grading systems cannot accurately represent any individual color such as the color of a diamond.
Therefore, the need arises for a method and system to provide accurate reference color for color grading of gemstones, to process the color data, to designate a color grade comprising of color names for verbal description and color coordinate or color notations for accurate color communication in the jewelry industry.